1. Field of the Invention
The invention relates to a positive-working radiation-sensitive mixture containing a) a polymeric binder having acid-labile groups and b) a compound which forms a strong acid on irradiation. It also relates to a radiation-sensitive recording material having a base and a radiation-sensitive coating produced from said mixture to be used for printing plates and photoresists.
The positive-working copying materials based on o-quinone diazides, in particular, have hitherto gained acceptance for such purposes. The photosensitivity of these materials is, however, frequently unsatisfactory. It can be increased by using catalytically active systems, since in such cases the quantum yield becomes greater than 1. Thus, the known principle of initiating subsequent reactions by means of photolytically produced acids in order to effect an increased solubility of the exposed areas has recently been exploited. In this case, photochemically produced strong acids catalyze the cleavage of acid-labile compounds whose cleavage products have a greater solubility than the original compounds in aqueous alkaline developers.
In positive-working radiation-sensitive mixtures, the acid-cleavable compounds used as low- and high-molecular-weight acetals and O,N-acetals containing aromatic compounds as hydroxyl or amine component (U.S. Pat. No. 3,779, 778), as are ortho esters and amide acetals (U.S. Pat. No. 4,101, 323), polymeric ortho esters (U.S. Pat. No. 4,311,782), polymeric aliphatic acetals (U.S. Pat. No. 4,247,611), enol ethers (U.S. Pat. No. 4, 248,957) or N-acyliminocarbonates (U.S. Pat. No. 4,250,247). To initiate the cleavage reaction, such mixtures require not only the photochemically produced acid, but also water, and this results in problems in their practical usability, in particular if irradiation is carried out at different atmospheric humidity.
Polymers containing acid-labile tert-butoxycarbonyloxy or tert-butoxycarbonyl ("tBOC") groups which work positively when mixed with photochemical acid donors are described in EP-A 0 102 450 and 0 366 590. Although such systems do not require water to initiate the cleavage reaction, they are also, however, not free of disadvantages. The thermal stability of the photosensitive layers produced therewith is unsatisfactory. In J. Polym. Sci. A 24, 2971 (1986), H. Ito diagnoses the autocatalytic cleavage reaction due to acidic phenolic hydroxyl groups contained in the polymer as the reason for this. To solve the problem, Ito proposes the synthesis of block copolymers in which tBOC and phenolic OH groups are spatially separated. However, that is a method involving expensive preparation. EP-A 0 264 908 describes a polymer in which the tert-butoxycarbonyl groups are replaced by less easily cleavable sec-butoxycarbonyl or isopropoxycarbonyl groups, but this results in losses in the photosensitivity.